A DNA transposable element is one kind of DNA repeat sequence, and are common in vertebrate genomes. However, most vertebrate transposable elements have lost their transposition activities. Among vertebrate DNA transposable elements, transposition activities have only been directly demonstrated in the zebrafish Tzf element (Lam W L, Lee T S, Gilbert W. (1996) Proc Natl Acad Sci USA 93: 10870-10875) and in the medaka fish (Oryzias latipes) Tol2 element (Transposable element of Oryzias latipes, no. 2) (Koga A., Suzuki M., Inagaki H., Bessho Y. and Hori H. (1996) Transposable element in fish. Nature 383: 30).
The Tol1 element is a DNA transposable element present in medaka fish and at 100 to 200 copies per genome (Koga A., Sakaizumi M., Hori H. (2002) Zoolog Sci 19: 1 to 6 (Non-patent Document 1)). This element was discovered as an insert into a mutant tyrosinase gene. The mutant tyrosinge gene has a phenotype of a complete albino body color (Koga A., Inagaki H., Bessho Y., and Hori H. (1995) Mol Gen Genet 249: 400-405. (Non-patent Document 2)). Tyrosinase is an enzyme essential in the biosynthesis of melanin. Tol2's transposition activity was demonstrated in Tol2 thereafter. Unlike Tol2, since excision and insertion was not directly detected in the Tol1 element, it was originally believed that the Tol1 element had already lost its transposition activity. In addition to the copy first discovered in a tyrosinase gene, other copies were also isolated and examined; however, none had the structure of a gene (Koga A., Inagaki H., Bessho Y., and Hori H. (1995) Mol Gen Genet 249: 400-405. (Non-patent Document 2)). This further contributed to the belief that Tol1 had lost its transposition activity.
In 2001, a fish from an albino subline was found to have partial pigmentation, i.e., a mosaic pigmentation. Analysis of this fish, demonstrated that the Tol1 element had been excised from its insertion site (Tsutsumi M., Imai S., Kyono-Hamaguchi Y., Hamaguchi S., Koga A. and Hori H. (2006) Pigment Cell Res 19: 243-247. (Non-patent Document 3)). Since Tol1 had been excised, it is a DNA transposable element and that had not lost its transposition activity. However, its de novo insertion in a chromosome had not been observed. Furthermore, no transfer enzyme (transposase) has been found.
Transposable elements are used in genetic engineering and in molecular biology applications. For example, transposable elements are used to mutagenize genes, promoters, enhancers, etc., and are expected to be useful in gene therapies, and the like. The Tol2 element, which was discovered in medaka fish genomes, has already been used in such applications (Koga A., Hori H., and Sakaizumi M. (2002) Mar Biotechnol 4: 6-11. (Non-patent Document 4), Johnson Hamlet M. R., Yergeau D. A., Kuliyev E., Takeda M., Taira M., kawakami K., Mead P. E. (2006) Genesis 44: 438-445. (Non-patent Document 5), Choo B. G., Kondrichin I., Parinov S., Emelyanov A., Go W., Toh W. C. and Korzh V. (2006) BMC Dev Biol 6: 5. (Non-patent Document 6), Japanese Patent Application Laid-Open (JP-A) No. 2001-218588 (Patent Document 1)). In addition to the Tol2 element, the Sleeping Beauty element was artificially constructed from debris present in salmon genomes (Lvics Z., Hackett P. B., Plasterk R. H., Izsvak Z. (1997) Cell 91: 501-510. (Non-patent Document 7), National Publication of International Patent Application No. 2001-523450 (Patent Document 2)); the Frog Prince element was similarly constructed from a frog genome (Miskey C., Izsvak Z., Plasterk R. H., Ivics Z. (2003) Nucleic Acids res 31: 6873-6881. (Non-patent Document 8), National Publication of International Patent Application No. 2005-527216 (Patent Document 3)); and the piggyBac element was isolated from an insect genome (Wu S. C., Meir Y. J., Coates C. J., Handler A. M., Pelczar P., Moisyadi S. and Kaminski J. M. (2006) Proc Natl Acad Sci USA 103: 15008-15013. (Non-patent Document 9)); each of these elements has been used in gene introduction, etc. These elements are characterized by high transposition frequency. This characteristic is important when they are to be used in genetic engineering or molecular biology applications. Tol1 is estimated to have a high transposition ability given the large number of pigmented cells in mosaically-pigmented medaka fish.    Patent Document 1: JP-A No. 2001-218588    Patent Document 2: National Publication of International Patent Application No. 2001-523450    Patent Document 3: National Publication of International Patent Application No. 2005-527216 [Non-patent Document 1] Koga A., Sakaizumi M., Hori H. (2002) Zoolog Sci 19: 1-6.    [Non-patent Document 2] Koga A., Inagaki H., Bessho Y., Hori H. (1995) Mol Gen Genet 249: 400-405.    [Non-patent Document 3] Tsutsumi M., Imai S., Kyono-Hamaguchi Y., Hamaguchi S., Koga A., Hori H. (2006) Pigment Cell Res Res 19: 243-247.    [Non-patent Document 4] Koga A., Hori H., Sakaizumi M. (2002) Mar Biotechnol 4: 6-11.    [Non-patent Document 5] Johnson Hamlet M. R., Yergeau D. A., Kuliyev E., Takeda M., Taira M., Kawakami K., Mead P. E. (2006) Genesis 44: 438-445.    [Non-patent Document 6] Choo B. G., Kondrichin I., Parinov S., Emelyanov A., Go W., Toh W. C., Korzh V. (2006) BMC Dev Biol 6: 5.    [Non-patent Document 7] Ivics Z., Hackett P. B., Plasterk R. H., Izsvak Z. (1997) Cell 91: 501-510.    [Non-patent Document 8] Miskey C., Izsvak Z., Plasterk R. H., Ivics Z. (2003) Nucleic Acids Res 31: 6873-6881.    [Non-patent Document 9] Wu S. C., Meir Y. J., Coates C. J., Handler A. M., Pelczar P., Moisyadi S., Kaminski J. M. (2006) Proc Natl Acad Sci USA 103: 15008-15013.